This invention relates to a fiber reinforced composite liner of flexible resin absorbent material, and more particularly to a composite liner having bundles of high-strength low-elongation fiber layers disposed circumferentially around the tubular liner adjacent to both inner and outer surfaces of the liner with at least one layer of resin absorbent material between the fiber reinforcing layers to increase the resistance to buckling of the cured liner.
It is generally well known that conduits or pipelines, particularly underground pipes, such as sanitary sewer pipes, storm sewer pipes, water lines and gas lines that are employed for conducting fluids frequently require repair due to fluid leakage. The leakage may be inward from the environment into the interior or conducting portion of the pipelines. Alternatively, the leakage may be outward from the conducting portion of the pipeline into the surrounding environment. In either case, it is desirable to avoid this leakage.
The leakage may be due to improper installation of the original pipe, or deterioration of the pipe itself due to normal aging or to the effects of conveying corrosive or abrasive material. Cracks at or near pipe joints may be due to environmental conditions such as earthquakes or the movement of large vehicles on the overhead surface or similar natural or man made vibrations, or other such causes. Regardless of the cause, such leakages are undesirable and may result in waste of the fluid being conveyed within the pipeline, or result in damage to the surrounding environment and possible creation of a dangerous public health hazard. If the leakage continues it can lead to structural failure of the existing conduit due to loss of soil and side support of the conduit.
Because of ever increasing labor and machinery costs, it is increasingly more difficult and less economical to repair underground pipes or portions that may be leaking by digging up and replacing the pipes. As a result, various methods had been devised for the in place repair or rehabilitation of existing pipelines. These new methods avoid the expense and hazard associated with digging up and replacing the pipes or pipe sections, as well as the significant inconvenience to the public. One of the most successful pipeline repair or trenchless rehabilitation processes that is currently in wide use is called the Insituform® Process. The Insituform Process for the cured in place pipe (“CIPP”) installation is described in U.S. Pat. Nos. 4,009,063, 4,064,211 and 4,135,958, the contents of all of which are incorporated herein by reference.
Flexible tubular liners suitable for use in the Insituform Process are generally flexible tubes of two or more layers of resin absorbent material. Typically the resin absorbent material is a needled felt of a synthetic fiber, such as polyester, but may be acrylic, polypropylene, or an inorganic fiber, such as glass or carbon. The cured-in-place-pipe liner generally includes two or more layers of resin absorbent material, but may include several layers, depending on the desired ultimate thickness of the liner and the diameter of the conduit to be lined. The inner tubular layer or layers are usually uncoated on both sides. The outer layer has an impermeable layer on the outer surface so that resin impregnated into the resin absorbent layers may be retained within the resin absorbent material. A method for producing such flexible tubular liners having at least two layers with the outer layer having an outer impermeable layer is described in detail in U.S. Pat. No. 5,285,741. The contents of this patent are incorporated herein by reference.
There are many suggestions in the prior art to reinforce a CIPP liner by addition of filamentary or other materials. The '063 Patent suggests attaching a scrim web to the filled layers. Similarly, in WO 91/14896 I suggest wrapping one or more reinforcement layers of a synthetic fiber and/or glass about an inner resin absorbent tube to increase the hoop strength of the resulting rigid pipe. An outer resin absorbent tube having an impermeable coating is disposed about the reinforcement layer or layers. It had been earlier suggested by Eric Wood in U.S. Pat. No. 4,836,715 to incorporate reinforcing layers near the inner and outer surfaces of the lining to simultaneously protect against buckling and ovality, respectively. The reinforcing fabric layers are provided in the form of fabric layers of glass and polyamide that extend generally circumferentially of the tubular lining. More recently, in U.S. Pat. No. 5,868,169 a layer of reinforcing fibers, such as fiberglass is encapsulated between layers of resin absorbent material saturated with resin. The reinforcing fibers in the form of a mesh or mat of fiberglass are fixedly attached to the inner and outer layers of resin absorbent material.
In the standard practice of the Insituform Process an elongated flexible tubular liner of a felt fabric, foam or similar resin absorbent material with an outer impermeable coating is impregnated with a thermosetting curable resin. Generally, the liner is installed within the existing conduit utilizing an eversion process, as described in the later two identified Insituform patents. In the eversion process, radial pressure applied to the interior of an everted liner presses it against and into engagement with the inner surface of the pipeline. The Insituform Process is also practiced by pulling a resin impregnated liner into the conduit by a rope or cable and using a separate fluid impermeable inflation bladder or tube that is everted within the liner to cause the liner to cure against the inner wall of the existing pipeline.
A curable thermosetting resin is impregnated into the resin absorbent layers of a liner by a process referred to as “wet out.” The wet-out process generally involves injecting resin into resin absorbent layers through an end or an opening formed in the outer impermeable film, drawing a vacuum and passing the impregnated liner through nip rollers as is well known in the lining art. One such procedure of this vacuum impregnation is described in Insituform U.S. Pat. No. 4,366,012, the contents of which are incorporated herein by reference. A wide variety of resins may be used, such as polyester, vinyl esters, epoxy resins and the like, which may be modified as desired. It is preferable to utilize a resin which is relatively stable at room temperature, but which cures readily when heated with air, steam or hot water, or subjected to appropriate radiation, such as ultra-violet light.
The CIPP flexible tubular liners have an outer smooth layer of relatively flexible, substantially impermeable polymer in its initial state. When everted, this impermeable layer ends up on the inside of the liner after the liner is everted during installation. As the flexible liner is installed in place within the pipeline, the liner is pressurized from within, preferably utilizing an eversion fluid, such as water, air, or steam to force the liner radially outwardly to engage and conform to the interior surface of the existing pipeline. Typically, cure is initiated by introduction of hot water into the everted liner through a recirculation hose attached to the end of the everting liner or by introduction of steam. The resin impregnated into the absorbent material is then cured to form a hard, tight fitting rigid pipe lining within the existing pipeline. The new liner effectively seals any cracks and repairs any pipe section or pipe joint deterioration in order to prevent further leakage either into or out of the existing pipeline. The cured resin also serves to strengthen the existing pipeline wall so as to provide added structural support for the surrounding environment.
While the present suggestions to increase strength and resistance to buckling of the cured liner are available, use of high modulus fiber layers substantially increase the cost of raw materials and introduce difficulties in handling webs and attaching them to one of the resin absorbent layers. Moreover, it has been found that placement of layers of reinforcing fiber between layers of resin absorbent material does not provide for sufficient increases in buckling resistance to justify the additional costs. Thus, the prior art does not teach a construction that allows obtaining the desired improvements by placing reinforcing fibers at the outside surfaces of the composite.
Accordingly, it is desirable to provide a reinforced liner that can provide increased resistance to buckling at a reduction in cost compared to liner presently utilized and disclosed in the prior art.